Spike or plug nozzles for rockets have long been known to have certain desirable characteristics for rocket propulsion. For example, they tend to be efficient over a greater altitude range than the conventional convergent-divergent type of nozzle; and they can be made to be much shorter in an axial direction, so that considerably more propellant can be packed into a rocket of a given length. Hence, by use of such a nozzle, a more powerful rocket can be made to fit into the allotted space in submarines and silos.
However, a long standing problem relating to use of spike nozzles has been means of controlling thrust of a rocket of steering, velocity control, and extinguishment of propellant for on-off operation.